FR3141055A1 - Simplified connected ECG watch - Google Patents

Abstract

A portable electronic device configured to be positioned on a wrist of a user and capable of performing an electrocardiogram (ECG) is provided. The device comprises exactly two ECG electrodes, the potential being imposed on one of the two ECG electrodes. The two electrodes consist of a first ECG electrode (220) on the middle part (210) and configured to be in contact with the skin of the wrist and a second ECG electrode. Figure for abstract: Fig. 7

Description

Simplified connected ECG watch

The present invention relates to the field of connected watches and in particular connected watches capable of performing an electrocardiogram (ECG or EKG). By watch, we mean a wearable device, the preferred position of which is the wrist . The present invention also relates to the field of so-called hybrid connected watches, that is to say connected watches having a visual appearance closer to conventional mechanical watches, in particular thanks to the presence of a gear train as well as mechanical hands to indicate at least the time (hour hand and minute hand).

An ECG is a measurement that allows you to study the functioning of the heart by measuring its electrical activity. An electrical impulse passes through the heart with each contraction and the ECG constitutes a trace obtained by recording the electrical potentials. The ECG is one of the main measurements for cardiovascular monitoring. Thanks to its integration into a watch, any user can regularly perform an ECG, which allows better analysis and prevention of cardiac risks. To perform an ECG, several electrodes are positioned on the human body, in order to detect different components of the electrical signals which are called leads or leads . In one of the simplest forms, the ECG provides a bipolar measurement between the right arm and the left arm, called lead I or DI.

The test is painless, passive and non-invasive (no current injection into the skin) and can be performed in less than a minute. Although the theoretical concept of integrating an ECG into a consumer device has been presented for several years (see in particular document US5289824), concrete and effective implementation has only been successful recently. This is a major technological innovation.

The document “ A Review of Methods for Non-Invasive Heart Rate
Measurement on Wrist ” (by Pinho Ferreira & Al, 2020) describes the state of the art regarding wrist-based cardiac measurements. This paper explains that unipolar measurement of the ECG from a single location on the human body would not be possible due to its differential nature, as well as the common mode of this signal which is floating and can vary significantly. To achieve the highest Signal to Noise Ratio (SNR), two electrodes are typically placed on either side of the heart, where cardiac action potentials occur. Unfortunately, the signal is quickly attenuated when the electrodes are moved away from the heart, and particularly if both electrodes are placed on the same side of the heart, such as along a single arm. However, if the measurement is taken from both hands, the amplitude remains high enough to conveniently extract the heart rate. Thus, the conventional approach is to place a device on the wrist which is to be touched by the other hand, thus ensuring electrical contact with the skin of both arms, as shown in Figure illustrating the state of the art: two electrodes (ECG_N and VCM) are placed under the device, in contact with the wrist of an arm (for example the left arm), and an upper electrode (ECG_P) allows a finger to be placed the opposite hand (for example that of the right arm).

Watches allowing you to perform an ECG (hereinafter called “ECG watches”) are few in number on the market in 2022. These include the Withings Move ECG, the Withings ScanWatch, the Apple Watch and the Samsung Galaxy.

As described above, these watches all use three ECG electrodes, in a similar configuration to the regarding the contacts between the arms and the electrodes. In particular, the one-lead ECG measurement (lead I) consists of measuring the difference in electrical potential between the left and right upper limbs. The three electrodes therefore consist of a negative electrode (ECG_N) in contact with one arm, a neutral electrode in contact with the same arm and a positive electrode (ECG_P) in contact with the other arm. This arrangement allows a simple and repeatable movement, by placing a single electrode in contact with the arm that must move. The role of the neutral electrode is to fix the body to a common mode (an average potential). This makes it possible to center the signal around an average potential, and to actively eliminate the noise commonly observed on both members, namely mainly electromagnetic interference due to electrical power sources (noise at 50 or 60Hz).

The implementation of an ECG measuring device in a watch presents numerous technical difficulties, in particular in that the electrical signals to be identified are of low amplitude and in that their acquisition is frequently noisy. The correct positioning of the electrodes and the management of the electrical chain between the electrodes and the electronic module which manages the ECG are crucial.

The invention aims to simplify the architecture of such an ECG watch in particular in order to limit noise sources, to limit mechanical parts and/or manufacturing steps, and to simplify electronic assembly.

For this purpose, the present description relates to a portable electronic device configured to be positioned on a user's wrist, the portable device making it possible to perform an electrocardiogram, ECG, said device comprising: a middle case, configured to be at least partially in contact with the skin of the wrist, the device further comprising exactly two ECG electrodes, the two ECG electrodes consisting of: a first ECG electrode, made of conductive material, on the back of the middle and configured to be in contact with the skin of the wrist wrist, a second ECG electrode, made of conductive material. To perform an electrocardiogram, the device further comprises an ECG electronic module, electrically connected to the first ECG electrode and to the second ECG electrode, and configured to impose a potential on one of the two ECG electrodes and to measure a potential of the the other of the two ECG electrodes, the potential of which varies depending on the user's heartbeat. The second ECG electrode is arranged on the portable electronic device so as to be able to be in contact with the user's arm opposite to the one which is in contact with the first ECG electrode.

In fact, a portable electronic device is proposed with only two ECG electrodes. The portable electronic device directly measures the potential difference between one of the two ECG electrodes, for example that in contact with the wrist, and an electrical potential imposed on the another electrode, for example the one incorporated in the bezel of the watch. The portable electronic device makes it possible to measure the potential difference between the variable potential at one of the two ECG electrodes, and a potential imposed on the other electrode, unlike a three-electrode configuration where the potential difference is calculated between two electrodes. Variable potential ECG. The imposed potential is typically constant, to simplify the electronic architecture.

This configuration with two ECG electrodes in a watch has not been proposed previously due to the need to limit electromagnetic interference due to electrical power sources. However, modern watches operate on reduced power from a battery internal to the watch. The continuous connection to a power supply network is then no longer necessary. The inventors had the idea of proposing a two-electrode architecture, despite the difficulties that such a solution may suggest. Indeed, apart from the question of interference, the arrangement of the two electrodes is necessarily different from the conventional architectures of watches with three ECG electrodes. Thus, the inventors developed an ECG watch architecture with only two ECG electrodes and they carried out test campaigns. They thus realized that, as long as the measurement is carried out without direct contact with a power source connected to the network, electromagnetic interference is minimal and does not require the presence of the neutral electrode. The inventors then proposed this new simplified architecture with two ECG electrodes to produce an ECG on a watch.

This architecture has many advantages. In fact, it allows the simplification of the architecture of the parts since only one electrode is required on the caseback, compared to two previously. This electrode is therefore optimized because an enlargement of its surface is made possible. In addition, the invention makes it possible to use fewer components in the electronic circuit while not suffering loss of amplitude by the injection of a common mode potential via the electrode with imposed potential.

In one embodiment, the device further comprises a middle part, a glass and a bezel mounted on the middle part and surrounding the glass, in which the bezel comprises a bezel body and the bezel body comprises the second ECG electrode.

In one embodiment, the bezel is movable in rotation relative to the middle part.

In one embodiment, the middle part comprises a side wall, the side wall comprising an opening in which a crown movable in rotation is inserted and/or be movable in translation, the ECG electrode being formed by the crown.

In one embodiment, the imposed potential is a constant potential. This simplifies the electronic architecture and the processing of electrical signals to generate an ECG.

In one embodiment, the ECG module is configured to impose the potential on the second ECG electrode.

In one embodiment, the ECG module is configured to impose the potential on the negative electrode.

In one embodiment, the ECG module comprises an analog front end capable of receiving a maximum voltage amplitude, the ECG module being configured to impose the constant potential at a value approximately equal to half of the maximum voltage amplitude.

In one embodiment, the ECG module is configured to impose the potential at a value between 0.5V and 2 V, in particular between 0.8V and 1.0V. In particular, the imposed potential is constant.

In one embodiment, the middle part comprises an optical sensor, the first electrode surrounding at least partly the optical sensor.

In one embodiment, the first electrode surrounds the optical sensor with an angular extent greater than 180°.

In one embodiment, the first electrode completely surrounds the optical sensor.

In one embodiment, the first electrode has an annular shape.

In one embodiment, the first electrode is in the form of a metal body.

In one embodiment, the first electrode is in the form of a metallic coating.

In one embodiment, the portable electronic device is a watch, the watch being for example a hybrid watch with mechanical hands.

The present invention also relates to a method for taking an electrocardiogram, ECG, using a device as defined above, during which the user places one arm in contact with the first ECG electrode and another arm in contact with the second ECG electrode.

The present invention also relates to the use of a device as previously described for carrying out an electrocardiogram.

Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

This figure shows a top view (in a Z direction) of the ECG watch, where the dial, the crystal and the bezel in particular are visible, according to a first embodiment (the hands are not shown).

This figure shows a view from below (in a Z direction) of the ECG watch, where the middle part and the middle part in particular are visible, according to the first embodiment.

This figure shows a sectional view along the XZ plane of an ECG watch, according to one embodiment.

This figure shows a diagram of the ECG watch with certain components, notably electronic ones.

This figure illustrates how the ECG watch works.

This figure shows a top view (in a Z direction) of the ECG watch according to a second embodiment.

This figure shows a bottom perspective view of the ECG watch according to the second embodiment.

This figure shows a bottom perspective view of ECG watches according to other embodiments.

These figures present comparative test results of the ECG watch according to the second embodiment with an ECG watch with a 3 ECG electrode configuration.

This figure illustrates an ECG watch according to the state of the art.

Detailed description of the embodiments

The present description relates to a portable electronic device comprising an electrocardiogram sensor (hereinafter: ECG sensor). In a particular embodiment, which is the one illustrated, the portable electronic device is a watch (hereinafter: ECG watch). The ECG watch may include a bracelet. However, for the purposes of this description, the term ECG watch does not necessarily include the bracelet, which is generally manufactured elsewhere and which can be assembled at points of sale.

The portable electronic device is connected, so that it can exchange data remotely (wirelessly) bidirectionally with a terminal, such as a smartphone. The connection can be made via Bluetooth, such as Bluetooth Low Energy (BLE). In particular, the data exchanged from the ECG watch to the terminal are ECG data acquired by the ECG watch. The ECG watch can also receive data via the terminal (time data, alarm data, notifications, etc.).

In one embodiment, the ECG watch is a hybrid watch, that is to say a watch with a dial and hands to indicate the hours and minutes.

Figures 1 to 3 represent an electronic ECG watch 100, of hybrid type (with a dial, mechanical hands, and possibly a screen integrated into the dial) according to a first example and Figures 6 to 7 represent an electronic ECG watch 100 according to a second example.

In the present description, the notion of “top”, “bottom” is defined in relation to the Z direction, the top being in the direction of the ice and the bottom being in the direction of the caseback, which will be described below .

The ECG watch 100 may comprise a middle part 110 and a middle part 210 which is configured to be at least partially in contact with the skin of the user's wrist. The middle part 110 and the middle part 210 are integral with each other. In one embodiment, as illustrated in the figures, the middle part 110 and the middle part 210 are two separate parts. In an embodiment not illustrated in the figures, the middle part 210 is a part integrated into the middle part 110. The middle part 110 may include a side wall 112, which is generally visible when the ECG watch 100 is worn on the wrist. The middle part 110 may include horns 114 (two pairs, on either side of the middle part 110) for attaching a bracelet (not shown in the figures). The middle part 110 may include a plurality of parts.

The ECG watch 100 can also include a glass 130 (“ glass ” or “ crystal ” in English), generally mounted on the middle part 110, so that the glass 130 is fixed. The lens 130 is or may comprise a typically transparent protective glass and may be made of glass, ceramic, plastic or any transparent material. The contour of the glass 130 is here typically circular in shape.

In the case of a hybrid watch, under the crystal 130, the ECG watch 100 further comprises a dial 132 with hands (physical hands, which are not shown in the figures). The dial 132 can also receive a screen 134 (for example with an opening in the dial which makes it possible to make visible a screen positioned just under the dial), which occupies for example a small space under or in the dial 132. The crystal 130 protects these parts and allows them to be seen through transparency.

In the case of an Apple Watch type “ smartwatch ”, under the glass 130, the ECG watch includes a screen, not shown here, which occupies a width close to the width of the ECG watch 100. In one embodiment , the screen may display hands. The glass 130 is then the protective glass of the screen.

The ECG watch 100 may also include a bezel 140 (“ bezel ” in English), mounted on the middle part 110. The bezel 140 is positioned around the glass 130 (radially external to the glass). The bezel 140 is an annular shaped part, essentially rotating around the Z direction (with a few modifications).

In the example illustrated in Figures 1 to 3, the bezel 140 is mounted to rotate relative to the middle part 110. The rotation can be done step by step (for example notch by notch). The user can thus rotate the bezel 140. Alternatively, in the example illustrated in Figures 6 and 7, the bezel 140 is fixed relative to the middle part 110. Thus in this variant, the bezel 140 is not rotary relative to the middle part 110.

There illustrates a sectional view of the ECG watch 100 according to the first example. The middle part 110 notably comprises a main body 310 (or middle body), which comprises the side wall 112. On the , the main body 310 comprises an opening 320 at the level of the side wall 112 to allow the installation of the crown 330. The crown 330 presents in particular a role of user interface between the ECG watch 100 and the user. To this end, the crown 330 can be movable in rotation (here around the axis X) and/or be movable in translation (here along the axis X).

The middle part 210 can be mounted on the main body 310. In the sectional view of the , the middle part 210 includes a recess 340, which is a positioning pad for a battery charging station. The middle part 110 may also include a bezel support 350, mounted on the main body 310. The bezel 140 is in particular mounted on the bezel support 350, in a radially external position. The glass 130 is also mounted on the telescope support 350, in a radially internal position.

The bezel 140 may comprise a bezel body 360, which is mounted on the middle part 110. The bezel body 360 may directly integrate (by engraving or otherwise) the traditional decoration of a watch, so that the bezel 140 is formed integrally. by the bezel body 360. Alternatively, as illustrated in , the bezel 140 further comprises a viewing ring 370 (also called “decor”) which can be mounted (for example by gluing, for example with double-sided adhesive) on an upper face of the bezel body 360. decor can then include visual markers.

The spectacle body 360 may be made of conductive material, such as metal (for example, stainless steel or titanium alloy). Alternatively, the 360 scope body may be made of charged plastic or conductive ceramics. Alternatively, the spectacle body 360 may not be conductive and a conductive coating is deposited on all or part of the spectacle body 360 (for example from the upper face or the external side face to the notches on the lower face). .

The ECG watch 100 includes an optical sensor 230, visible in . The optical sensor 230 comprises at least one light source (for example an LED), for emitting light, and at least one photodiode, for receiving light. The optical sensor 230 is typically a PPG (photoplethysmography) sensor. The optical sensor 230 can be positioned behind a lens 240, for example made of glass, which comes to the interface of the skin of the wrist. Document PCT/EP2021/058955, on behalf of Withings, describes in detail the optical sensor, which is found on the Withings ScanWatch.

To recover the electrical signals generated by the human body, the ECG watch 100 includes an ECG sensor. The ECG sensor includes in particular a set of electrodes (called ECG electrodes and described in detail below) and an electronic module ECG 300 (shown schematically on the ), to which the ECG electrodes are electrically connected.

By electrode is meant a conductive part capable of receiving or transmitting an electric current, an electric potential or an electric voltage. The part may be made of conductive material or include a conductive coating. By “conductor” it is meant “conductor of electricity”.

According to the present description, the ECG watch 100 comprises exactly two ECG electrodes making it possible to perform an ECG, including a first ECG electrode and a second ECG electrode. Thus, unlike conventional ECG watches which require three ECG electrodes in order to produce an ECG, the present description proposes to simplify the architecture of the ECG watch 100, as will be explained in more detail later.

As visible in Figures 2 and 3, the first ECG electrode 220 is located on the middle part 210 in order to be in contact with the skin of the wrist of the user on which the latter wears the ECG watch 110. The first electrode 220 is electrically connected to the ECG module 300. The first ECG electrode 220 can surround at least partly the optical sensor 230.

The first electrode 220 is made of conductive material, such as metal (for example stainless steel or titanium alloy). In the example illustrated in Figures 1 to 3, the first electrode 220 is in the form of a metal body. By metal body, we mean a part whose maximum thickness is greater than 0.1 mm.

In the variant illustrated by Figures 6 and 7, the first electrode 220 can be formed by a conductive coating deposited on a surface (which is itself conductive or non-conductive). In particular, the first electrode 220 is in the form of a metallic coating on the lens 240 where the optical sensor 230 is located.

In the two examples illustrated in Figures 1 to 7, the first electrode 220 has an annular shape.

In the examples illustrated, the first electrode 220 surrounds at least partly the optical sensor 230. In particular, the first electrode 220 can completely surround the optical sensor 230 as visible in Figures 2 and 7.

There illustrates other examples of arrangements for the first electrode 220.

In example (A) of the , the first electrode 220 can extend around the optical sensor 230 over an angular extent less than 180°, for example 90°. The first electrode 220 is shown at the top in the Y direction, but can alternatively be located anywhere around the optical sensor 230.

In example (B) of the , the first electrode 220 can extend around the optical sensor 230 over an angular extent greater than 180°, but less than 360°, for example approximately 270°. The first electrode 220 is shown at the top in the Y direction, but can alternatively be located anywhere around the optical sensor 230.

In example (C) of the , the first electrode 220 and the optical sensor 230 can be formed by two half-disks facing each other. The first electrode 220 is shown on the left in direction X, but can alternatively be located on the right in direction X.

In example (D) of the , the ECG watch 100 does not include an optical sensor 230 and the first electrode 220 is in the form of a disc placed substantially in the center of the caseback 210.

The second electrode 170 is also electrically connected to the ECG module 300.

As visible in Figures 1 and 3, the second ECG electrode 170 can be located on the bezel 140 so that it can easily be in contact with the skin of the user's other hand. As illustrated in the figures, the second electrode 170 is the bezel body 360, that is to say that the entire bezel 140 or part of the bezel (accessible by the user) forms the electrode 170 The user can thus touch the bezel anywhere. Compared to a crown acting as an electrode, the ECG watch 100 can be worn on the left hand or the right hand indifferently, without the gestures to be made to perform an ECG being the same for a user wearing the watch on the left or on the right (symmetry of use), unlike the crown electrodes described in the introduction.

Alternatively, as illustrated in example (E) of the , the second ECG electrode 170 is formed by the crown 330. In order to carry out an ECG measurement, the user then places his free hand in contact with the crown 330.

Alternatively, in an example not illustrated, the second electrode is located or is part of a button present in the middle.

The second electrode 170 is made of conductive material, such as metal (for example stainless steel or titanium alloy). In the examples illustrated, the second electrode 170 is in the form of a metal body.

The middle part 110 (and in particular the middle part 210, the dial 132 and the main body 310 of the middle part 110) defines an internal volume 380 capable of receiving different components, such as electronic components. These electronic components are thus protected from water or dust (with appropriate sealing, in particular permitted by the aforementioned seals).

The ECG 300 module is shown schematically in dotted lines on the and positioned schematically. The two ECG electrodes 220, 170 are electrically connected to the ECG module 300. The ECG module 300 is configured to recover electrical signals coming from the human body and to, after processing, generate an electrocardiogram. The ECG module 300 can be mounted on an electronic card 380 (shown schematically in dotted lines on the and positioned schematically), printed circuit board type, where other elements of the ECG watch are also mounted.

The ECG 300 module notably includes an analog front-end (AFE for “ Analog front-end ”, in English). The analog front end is configured to receive at two inputs (a positive input and a negative input) the signals coming respectively from the two ECG electrodes 220, 170 (which are thus defined as a positive electrode and a negative electrode) and provide as output an ECG signal. The analog front end is for example the AD8233 offered by Analog Devices. The analog front end accepts a maximum voltage amplitude, corresponding to the supply voltage of the analog front end. Typically, this maximum amplitude can be between 1V and 4V, for example around 1.8V.

The ECG 300 module is configured to impose a potential on one of the two ECG electrodes. The potential is notably imposed by the analog front end in a passive manner. The imposed potential is advantageously a constant potential. In one embodiment, the constant potential is equal to approximately half the maximum voltage amplitude of the analog front end. By approximately, we mean plus or minus 10% of the value. In particular, the imposed potential is between 0.5V and 2V, for example between 0.8V and 1.0V, in particular 0.9V.

Indeed, if a potential was not imposed on one of the two ECG electrodes, the two ECG electrodes would be left “floating”, that is to say they would not be connected to a reference value. There would indeed be a difference in potential amplitude between the two electrodes, but the individual potentials could take a multitude of values. However, as explained previously, the analog front end accepts a limited voltage amplitude. In the example in which this maximum amplitude is approximately equal to 1.8V, imposing the constant potential at approximately 0.9V on one of the two electrodes makes it possible to bring the measurement within the amplitude acceptable for the ECG module 300. measurement will then oscillate around 0.9V, and will be measurable by the analog front end. Thus, the inventors have determined that by placing oneself at half the maximum amplitude, the acquisition of deviations is optimized upwards or downwards.

Advantageously, the ECG module 300 imposes the potential on the second ECG electrode 170, which is configured to be in contact with the arm opposite to that which carries the ECG device 100. Thus, unlike a conventional configuration with 3 ECG electrodes where the reference electrode is placed on the back of the middle, the ECG 300 module imposes the potential on the ECG electrode placed in contact with the free hand (that is to say the hand linked to the wrist where the watch is not located ). In particular, the ECG module 300 is configured to impose the potential on the negative electrode, which is in particular the second ECG electrode 170. The inventors realized that imposing the potential on the electrode in contact with the free hand allows to reduce the potential fluctuations induced by the contact of this free hand with the bezel and to reduce the micro-variations induced by the nervous system (unlike the contact between the first electrode 220 on the middle part and the arm on the on which the ECG device 100 is mounted, in particular because the arm remains immobile and inactive during the measurement).

The potential at the other electrode is left free by the ECG module 300. In this way, the potential of this electrode corresponds to the potential of the user's body (when there is contact) and varies depending in particular on the beats of the heart of the latter. Advantageously, the ECG module 300 leaves the potential of the first electrode 220 free.

The optical sensor 230 is connected to a PPG module 390, also positioned in the internal volume, which can also be mounted on the electronic card 380 of the ECG watch 100. The PPG module 390 is configured to generate the instructions intended for the light sources of the optical sensor 230 and to recover the electrical signals from the photodiodes.

A control unit 395 makes it possible to control the electronics on board the ECG watch 100. The control unit 395 can for example include or partially include the ECG module and the PPG module.

As shown in which schematically illustrates the device 100, the control unit 395 may comprise one or more processor(s) 410 and a memory 420 which stores instructions capable of being executed by the processor 2302.

The ECG watch 100 can also include an accelerometer 430, connected to the control unit 395 (for monitoring sleep, activity, etc.).

To supply the various components with electrical energy, the ECG watch 100 includes a battery 440, for example a cell or a rechargeable battery. The battery 440 is configured to power the ECG module 300 in particular. The recess 340 described previously makes it possible to place the middle part 210 on a charging station to recharge the battery 440.

The ECG watch 100 includes a wireless communication module 450, such as a Bluetooth module or Bluetooth Low Energy or a Wi-Fi module or a cellular module (GSM, 2G, 3G, 4G, 5G, Sigfox, etc.) , which allows it to communicate bidirectionally with at least one external terminal 460, such as a mobile telephone. The external terminal 460 can then communicate (bidirectionally) with a remote server 470 for data storage and processing. Alternatively or additionally, the wireless communication module 440 can communicate directly with the remote server 470, for example via the cellular network or via a Wi-Fi network. The data obtained by the ECG watch 100, such as an electrocardiogram, but also indications of heart rate, activity or oxygen saturation are transmitted to the external terminal 460 via the wireless communication module 440. The control unit 395 can process certain signals before sending them, to limit the size of the data.

The PPG module 390 and the ECG module 300 are also connected to the control unit 395 or are integrated and/or partially integrated therein. The ECG module 300 is known per se and will not be described in detail. Different types of electronic components can be included in the ECG 300 module (processor, resistor, capacitor, etc.).

The operation of the ECG watch 100 will be explained subsequently, with reference to the .

The ECG watch 100 is initially on a user's wrist. The user then selects the ECG measurement program, for example via crown 330 and screen 134.

Then, the user places at least one finger as illustrated in , or the palm of his hand, on the second ECG electrode 170 formed in the example illustrated by the bezel 140. The measurement of the ECG is thus carried out in a very simple manner for the user who only has to place his hand on the bezel 140.

A potential is imposed on one of the two ECG electrodes during a step 510. Advantageously, the potential is imposed by the ECG module 300 on the second ECG electrode 170, which is the ECG electrode placed in contact with the free hand (i.e. the hand tied to the wrist where the watch is not located, i.e. the hand that can potentially move during the measurement and disrupt the signals). By imposing the potential on this hand, the quality of the ECG is improved.

The potential at the other electrode is left free by the ECG module 300. In this way, the potential of this electrode corresponds to the potential of the user's body (when there is contact) and varies depending in particular on the beats of the heart of the latter. In a step 520, the potential of the first electrode 220 in contact with the user's wrist is measured. This wrist is generally very immobile and not muscularly used during the ECG measurement. Consequently, the signals obtained by the first electrode 220 can be of better quality.

Steps 510 and 520 can be implemented in parallel.

Then, during step 530, the ECG module 300 measures the difference in potentials between the first electrode 220 in contact with the wrist and the electrical potential imposed on the second electrode 170 incorporated in the bezel 140.

Then, in a manner known per se, the difference in potentials is amplified, filtered, digitized and analyzed by the ECG module 300 during a step 540.

Finally, during a step 550, the result is for example displayed on the screen 134. Alternatively or in addition, the result is sent to the external terminal 460 and/or to the remote server 470. A notification can then be sent to the user, on the screen 134 for example or on the external terminal 460.

Comparative tests

Figures 9 and 10 illustrate performance results of the ECG watch 100 illustrated in Figures 6 and 7. However, those skilled in the art will understand that these results apply in a similar manner to the ECG watch 100 illustrated in the figures. figures 1 to 3.

The ECG signals recorded by the ECG watch 100 according to the invention with the new 2-electrode ECG configuration are compared to the ECG signals measured by a watch with a classic 3-electrode configuration. The prototype watches used have identical mechanics, architecture and electronic components. Only the configuration of the ECG electrodes varies. In addition, each measurement by a watch prototype was carried out simultaneously with a reference ECG measurement with a reference device (Schiller).

On graph (A1) of the , the ordinate represents the number of ECG recordings (40 in total) made with a watch and the abscissa represents the root mean squared error (RMSE) of a watch- ECG 100 conforming to the second embodiment compared to a reference electrocardiogram (Schiller Cardiovit FT-1). “ Mean ” means the average and “ std ” means the standard deviation.

The RMSE is calculated relative to the Schiller reference signal: with N the number of points in the signal and ei the error at point i, corresponding to the difference between the Schiller reference signal and the watch signal tested at point i.

On graph (A2) of the , the ordinate represents the number of ECG recordings (40 in total) made with a watch and the abscissa represents the root mean squared error (RMSE) of a watch presenting a 3-electrode configuration compared to a reference electrocardiogram (Schiller Cardiovit FT-1).

On graph (B1) of the , the ordinate represents the number of ECG recordings (40 in total) made with a watch and the abscissa represents the signal to noise ratio (“Signal to Noise Ratio”, SNR, in English) of a watch- ECG 100 conforming to the second embodiment compared to a reference electrocardiogram (Schiller Cardiovit FT-1).

Signal-to-Noise ratio quantifies the noise level in the ECG signal. It is expressed in decibels (dB) and is calculated as follows: SNR = 10 ∗ log(S/N), with S the signal power (S=s ² /8) and N the noise power (N= n ² ).

In this metric, the “signal s” is calculated as the amplitude of the QRS complex (over a window of 100ms), and the “noise n” as the standard deviation of the supposedly flat part of the ECG signal (a window of 200ms, which begins 250 ms before each QRS complex detected).

On the graph (B2) of the , the ordinate represents the number of ECG recordings (40 in total) made with a watch and the abscissa represents the signal to noise ratio (“Signal to Noise Ratio”, SNR, in English) of a watch presenting a 3-electrode configuration compared to a reference electrocardiogram (Schiller Cardiovit FT-1).

On the graph (C1) of the , the ordinate represents the number of ECG recordings (40 in total) made with a watch and the abscissa represents the amplitude of the ECG signal of an ECG watch 100 conforming to the second embodiment compared to a reference electrocardiogram (Schiller Cardiovit FT-1).

On the graph (C2) of the , the ordinate represents the number of ECG recordings (40 in total) made with a watch and the abscissa represents the amplitude of the ECG signal from a watch with a 3-electrode configuration compared to a reference electrocardiogram ( Schiller Cardiovit FT-1).

On the graph (D1) of the , the ordinate represents the number of ECG recordings (40 in total) made with a watch and the abscissa represents the amplitude of the noise of an ECG watch 100 conforming to the second embodiment compared to an electrocardiogram reference (Schiller Cardiovit FT-1).

On the graph (D2) of the , the ordinate represents the number of ECG recordings (40 in total) made with a watch and the abscissa represents the amplitude of the noise of a watch with a 3-electrode configuration compared to a reference electrocardiogram (Schiller Cardiovit FT-1).

With reference to all the metrics calculated and represented in Figures 9 and 10, we observe that the results obtained by the ECG watch 100 are no worse than those obtained with a watch with a 3 electrode configuration. One such watch with 3 ECG electrodes is notably a ScanWatch 38mm, which, in 2019, obtained CE certification for ECG measurement.

Claims (15)

Portable electronic device (100) configured to be positioned on a wrist of a user, the portable device (100) making it possible to perform an electrocardiogram, ECG, said device comprising:

• a middle part (210), configured to be at least partially in contact with the skin of the wrist,
• exactly two ECG electrodes, the two ECG electrodes consisting of:
  • a first ECG electrode (220), made of conductive material, on the middle part (210) and configured to be in contact with the skin of the wrist,
  • a second ECG electrode (170), made of conductive material,
• an ECG electronic module (300), electrically connected to the first ECG electrode (220) and the second ECG electrode (170), and configured to impose a potential on one of the two ECG electrodes (220, 170) and to measure a potential of the other of the two ECG electrodes (140, 170), in order to perform an electrocardiogram.

Device according to claim 1, further comprising a middle part (110), a glass (130) and a bezel (140) mounted on the middle part (110) and surrounding the glass (130), in which the bezel (140) comprises a glasses body (360) and the glasses body (360) includes the second ECG electrode (170). Device (100) according to claim 1, in which the middle part (110) comprises a side wall (112), the side wall (112) comprising an opening (320) in which is inserted a crown (330) movable in rotation and/ or be movable in translation, the ECG electrode (170) being formed by the crown (330). Device (100) according to any one of the preceding claims, in which the imposed potential is a constant potential. Device (100) according to any one of the preceding claims, wherein the ECG module (300) is configured to impose the potential on the second ECG electrode (170). Device (100) according to any one of the preceding claims, in which the ECG module (300) comprises an analog front end capable of receiving a maximum voltage amplitude, the ECG module (300) being configured to impose a constant potential at a value approximately equal to half of the maximum voltage amplitude. Device (100) according to claim 6, in which the ECG module (300) is configured to impose a potential at a value between 0.5V and 2 V, in particular between 0.8V and 1.0V. Device (100) according to any one of the preceding claims, in which the middle part (210) comprises an optical sensor (230), the first electrode (220) at least partly surrounding the optical sensor (230). Device (100) according to claim 8, wherein the first electrode (220) surrounds the optical sensor (230) an angular extent greater than 180°. Device (100) according to claim 8 or 9, wherein the first electrode (220) completely surrounds the optical sensor (230). Device (100) according to any one of the preceding claims, wherein the first electrode (220) has an annular shape. Device (100) according to any one of the preceding claims, wherein the first electrode (220) is in the form of a metallic body. Device (100) according to any one of the preceding claims, wherein the first electrode (220) is in the form of a metallic coating. Device (100) according to any one of the preceding claims, in which the portable electronic device (100) is a watch, the watch being for example a hybrid watch with mechanical hands. Method for taking an electrocardiogram, ECG, using a device (100) according to any one of the preceding claims, during which the user places an arm in contact with the first ECG electrode (220) and a other arm in contact with the second ECG electrode (170).